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June 4, 2012 (Chicago) -- Taking a break from hormone therapy can shorten the lives of some men with metastatic prostate cancer, researchers say.

Many men take a break from hormone therapy -- aka androgen-deprivation therapy or ADT -- to lessen its often debilitating side effects.

ADT -- which turns off production of the male hormone testosterone that fuels the growth of prostate tumors -- is a first line of treatment for metastatic disease (that has spread beyond the prostate).

But because hormone therapy blocks male hormones, it can lead to loss of sexual function and severe hot flashes. Over time, weakened bones (osteoporosis) and heart problems may develop.

But in a new study of more than 1,500 men tracked for nearly a decade, patients with minimal cancer spread given continuous ADT lived an average of about two years longer than those given intermittent (on-again, off-again) ADT.

Interrupted ADT should no longer be recommended as an initial treatment, says researcher Maha Hussain, MD, of the University of Michigan Comprehensive Cancer Center in Ann Arbor, Mich.

"Continuous therapy continues to be the standard of care," she tells WebMD.

Hussain reported the findings here at the annual meeting of the American Society of Clinical Oncology.

Intermittent ADT

Prostate cancer is the second most common cancer in men, with nearly 242,000 cases diagnosed each year in the U.S., according to the American Cancer Society. Skin cancer is the most common.

Previous smaller studies suggested that intermittent hormonal therapy -- stopping and restarting treatment periodically -- was as effective as continuous therapy, but with a lower risk of these side effects, says Bruce Roth, MD, a prostate cancer specialist at Washington University School of Medicine in St. Louis. Roth, who was not part of the study, moderated a news briefing at which the findings were presented.

As a result, interrupted ADT became widely used in the U.S., he tells WebMD.

"But this study for the first time indicates that there is a price to pay. Men need to ask themselves if they are willing to trade hot flashes for two years of their lives," he says.

Continuous ADT Beats Out Intermittent ADT

The late-stage international study involved men with hormone-sensitive cancers that had spread beyond the prostate. All were given androgen deprivation therapy with Zoladex and Casodex for seven months. Men who responded were divided into two groups, with one staying on continuous ADT and the other getting intermittent treatment. They were tracked for an average of more than nine years.

Men given continuous therapy lived an average of nearly six years, compared with about five years for men getting intermittent therapy.

Men with minimal disease spread (no cancer beyond the spine, pelvis, and lymph nodes) on continuous therapy lived an average of about seven years vs. five years for those treated intermittently -- a striking two-year difference, Hussain says.

Among men with more extensive disease spread, the gap in survival narrowed: about four-and-a-half years for continuous therapy vs. five years for intermittent treatment.

But Hussain says that even these men should not be offered treatment breaks, as further study is needed.

Overall, the men who got the stop-and-start treatment received about half the amount of hormone therapy as men who got continual ADT, says researcher David I. Quinn, MBBS, PhD, of the University of Southern California in Los Angeles.

As a result, intermittent therapy costs about half as much as continuous therapy, which he estimated at $340 to $440 a month for the two drugs used in the study. Both drugs are covered by insurance, Quinn says.

These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.